Cook your pasta according to package directions, drain, return to pot and add butter.  Add cornstarch to grated cheddar cheese.  Then add cheese mixture, together with evaporated milk to pasta and return to medium heat.  Stir constantly until thick and smooth.  If you want a thinner sauce then add a tablespoon of milk at a time until it is to desired thickness. Add seasonings {more or less to taste} and serve with extra shredded cheese if desired.  Serve immediately.